Peter Grier is The Christian Science Monitor’s Washington editor. In this capacity, he helps direct coverage for the paper on most news events in the nation’s capital.

Did President Obama break the law by swapping five Taliban prisoners detained at the US Guantánamo Bay prison for Army Sgt. Bowe Bergdahl’s freedom? That’s what some critics of the deal insist. At issue is a statute which requires the president to give Congress 30 days notice before the release or transfer of Guantanamo prisoners. By its own account, the administration did not provide lawmakers with such advance notification.

“We have consulted with Congress for quite some time about the possibility that we might need to execute a prisoner exchange in order to recover Sergeant Bergdahl,” Mr. Obama told reporters at a stop in his five-day European trip. “We saw an opportunity. We were concerned about Sergeant Bergdahl’s health.”

The law in question was enacted as part of the 2014 National Defense Authorization Act (NDAA). When he signed that bill into law Obama included a signing statement which warned he might do what he just did.

“The executive branch must have the flexibility … to act swiftly in conducting negotiations with foreign countries regarding the circumstances of detainee transfers,” said the statement at the time.

Here’s the problem: By themselves, signing statements have no legal force. It may seem odd that Congress didn’t include a little wiggle room for emergency contingencies in regards to prisoner handling, but it didn’t. Some legal analysts thus conclude that it’s pretty clear the swap was illegal under the NDAA language.

The argument doesn’t end there, however. What if the law in question is itself unconstitutional? After all, the president of the United States is also the nation’s commander in chief under the Constitution (Article II, Section 2, Clause I). That invests him with enormous military powers, particularly in regards to tactical and strategic decisions. What if Congress passed a law requiring a 30-day notice before a president could order troops to patrol? That would pretty clearly be unconstitutional. Some analysts argue that a decision to repatriate a captured soldier isn’t much different.

But Professor Goldsmith adds that this a hard legal issue with few precedents. And some other legal experts think the constitutional argument in favor of Obama’s move is not in fact viable.

Congress pretty clearly can make some general rules in regards to the armed forces – it can pass laws meant to prevent US troops from using chemical weapons, for example. Enacting legislation that requires advance notice for moving any Guantánamo prisoner is that sort of general rule, argues George Mason University School of Law professor Ilya Somin.

The Guantánamo statute “is not like saying that the president must defend Hill X, but not Hill Y. This is like limiting the range of weapons or tactics that can be used to defend any hill located in a particular part of the world. That sort of restriction is at the very heart of Congress’ power to make rules for the government and regulation of the armed forces,” Professor Somin writes at “The Volokh Conspiracy” legal blog.

So what’s going to be done about this? In the end, Congress will hold hearings, and the GOP-controlled House will make some noise. There will likely be attempts to attach clarifying language to upcoming defense bills. But it’s pretty hard for the legislative branch to force the president to act in such a gray area. It’s really a political issue as much as a legal one.

The release of the last American prisoner of war in Afghanistan has reopened the mystery of how he was captured — and whether he’s a patriot or a deserter.

Even before Army Sergeant Bowe Bergdahl arrives home in the U.S. after almost five years in captivity, scores of soldiers, veterans and others have lit up social media with postings denouncing the former prisoner for allegedly abandoning his unit.

The U.S. Army has never described the circumstances of Bergdahl’s disappearance from a remote outpost in eastern Afghanistan or his capture by terrorists. An online petition drive that has more than 5,600 digital signatures calls on the Obama administration to punish Bergdahl for going AWOL, or absent without leave.